Electrodeposition of copper from an acid bath



United States Patent ELECTRODEPOSITION OF COPPER FROM AN ACID BATH Henry Brown, Huntington Woods, and Richard A. Fellows, Grosse Pointe, Mich., assignors to The Udylite Corporation, Detroit, Mich., a corporation of Delaware No Drawing. Application May 26, 1952, Serial No. 290,091

14 Claims. (Cl. 204-52) This invention relates to the electrodeposition of copper from an aqueous acidic bath and more particularly concerns the utilization of selected addition agents to aqueous acidic baths for the purposes hereinafter stated.

The primary object of this invention is to decrease the grain size and increase the luster of the copper deposit without materially imparing the ductility of the plate or decreasing the current density range of the acidic copper plating bath.

It has been found that fine grained as well as ductile copper piate may be electrodeposited from acidic copper baths and especially acidic copper sulfate baths when small concentrations of organic compounds having a structure characterized by the Formula A are added to the baths:

FORMULA A R1 R1 R2 N N=NZ R. N

wherein R1 and R2 may be hydrogen, methyl or ethyl radicals, X is an anion selected from the group consisting of chloride, bromide, iodide, fluoride, sulfate, bisulfate and nitrate; and Z is an aromatic radical selected from the group consisting of phenyl, naphthyl, and phenyl and naphthyl radicals substituted with amino, alkyl substituted amino, hydroxy and alkoxy substituent groups.

The anion X is relatively unimportant and in addition to the anions above given may be any one of a wide variety of other anions, including organic anions such as formate, acetate, propionate, etc. It will be appreciated that the compounds represented by the above formula, when present in an acid copper bath, are highly ionized substances and the anion X is in ionic admixture with the other anions of the bath such as the sulfate anion, the nitrate anion, etc. It is believed that the diamino phenylphenazonium nucleus or ion is the dominant contributor to the beneficial effects of decreasing the grain size without materially impairing ductility of the plate which is obtained from the presence in the bath of any of the compounds of Formula A.

In general, it is, preferred that the phenyl or naphthyl radicals be substituted with amino or alkyl substituted amino groups, that the alkyl groups be either methyl or ethyl groups, and that the alkoxy group be methoxy or ethoxy; and for best bath life it is preferable to maintain a concentration of chloride, or its equivalent in bromide or iodide, of about .003 to about .020 gram/liter in the solution. It is to be understood that when X is either fluoride, sulfate, bisulfate or nitrate, that chloride, bromide or. iodide ions in an amount equivalent to about .003to .020 gram/liter of chloride is preferably present in addition. As initially made up, a solution containing a compound in which X is a halide other than fluoride,

2,707,166 Patented Apr. 26, 1955 contains a sutficient halide concentration, but it is usually preferable to replenish the halide during use in order to maintain the preferred minimum concentration of about .003 gram/liter of chloride or its equivalent.

An outstanding example and a preferred representative of the class of compounds covered by the hereinabove given formula is the dye commercially known as Janus Green B. Janus Green B is sometimes designated Dia zine Green (Schultz #282) and chemically it may be designated briefly as diethyl-safranine-aZo-dimethyl-aniline. Another preferred example which is not generally as commercially available as Janus Green B, is represented by the above formula wherein R1 is hydrogen and R2 is a irfethyl radical, that is, dimethyl safranine azo dimethyl ani me.

The extremely useful addition agents represented by Formula A which efiectively accomplish the above stated object may, in general, be classified as the product of the coupling reaction of a diazotized amino phenazine with phenol, naphthol or aryl amino compounds including the alkyl substitution products of phenol, naphthol, or aryl amino compounds. Janus Green B, which is a diazotized amino phenazine coupled with dimethyl aniline, may be replaced by a diazotized amino phenazine coupled with other amino compounds such as substituted diethyl anilines and naphthylamines.

Illustrative examples of addition agents which fall in the class of compounds above described, which may be utilized in accordance with this invention and in the ranges of proportions indicated, are given in Table l.

Mixtures of the dyes shown in Table 1 may also be employed with beneficial effects. Where mixtures are employed, the total concentration of the mixed dye in the acidic aqueous bath preferably approximates the concentration of any component as indicated in Table 1. For example, Janus Green B may be mixed with Janus Black in a total concentration corresponding approximately to the concentration for either Janus Green B or Janus Black as given in Table 1. For general purposes, concentrations of the dyes of Table 1 falling within the range of .005 to .04 gram/liter, represent preferred quantities. Janus Green B is commercially available in approximately 50% dye strength in admixture with an inorganic salt, but it is to be understood that the concentrations set forth herein and in the appended claims refer to dye strength.

The composition of the acidic copper bath may vary over rather wide limits, although for the best grain refinement, rate of brightening and for the widest bright plating range, the following composition, designated Formula taining proportions of addition agents indicated in Table 1 include controlled temperatures, bath agitation and cathode current densities. For example, the bath temperatures may be from about 17 C. to 40 C. (approximately 70 F. to F.). Warmer temperatures above 40 C. tend to decrease the brightness of the plate, but temperatures up to 50 C. may be used satisfactorily. Cathode agitation and preferably uniform air agitation is desirable. Cathode current densities of 10100 amps./ sq. ft. (approximately 1-l0 amps/sq. dm.) may be satisfactorily employed with the particular current density depending primarily upon the degree of agitation of the cathode film and the shape of the article to be plated. For general purposes an average cathode current density of 30-50 amps/sq. ft. may be used.

Table 1 Oone., g1 runs/liter grams/met H;G CH:

H N --N=N-- N CH .0015-.05 .015

N ol Diethyl aatranlue azo dimethyl aniline-J anus Green B IEhC- -GH: (C|H|):N N=NOOH Dlethyl sairanine azo phenol-Janus Black 1110- OH: OH

H;N N=N Sairanine azo uaphtol-J anus Blue 4. Janus Gray (Color Index 137, Society of Dyers and Colourists, by

F. M. Rowe, 192 .0015-. 05 .015 5. Dimethyl safranine azo dimethyl aniline 0015. 05 015 As a substitute for the sulfuric acid of Formula B, nitric acid or phosphoric acid may be used in approximately equivalent proportions. Additionally, Formula B may include other ions for the purpose of increasing the conductivity of the solution such as sodium, potassium or ammonium ions. These ions are usually present in only minor concentrations. Furthermore, the copper sulfate of Formula B may be replaced by copper nitrate in approximately equivalent proportions, and when acidified with small amounts of phosphoric acid, nitric acid or sulfuric acid, the beneficial effect of reducing the grain size and increasing the luster of the deposit by additions of small concentrations of compounds of the type shown in Table 1 is also evident. The degree, however, of grain size, reduction and increase in luster is somewhat less extensive than is produced from the use of acidic baths made up primarily of copper sulfate. In general, the

copper sulfate or copper nitrate concentration in the bath may satisfactorily vary from as low as about 100 grams/liter up to saturation. Concentrations of acid above the equivalent in acidity of about 80-100 grams/ liter of sulfuric acid decrease the brightening effect of the addition agents represented by Formula A and are therefore to be avoided.

Small concentrations of wetting agents may be advantageously present in the baths of this invention. For example, the surface-active compounds, sodium decyl sulfate and the sulfated mono-ethylene oxide condensate of decyl alcohol when present in small concentrations of about .01 to .06 gram/liter are effective in decreasing pitting and striation formation in the deposit due to the presence of harmful organic compounds or excessive concentrations of brighteners. These wetting agents normally cause excessive frothing with air agitation, but in the presence of the addition agents of Table l, the frothing is minimized.

The following typical plating baths are given by way of example to illustrate the invention in greater detail. In each of the examples, the concentration of the-addition agent is given in strength.

Example I CuSOaSHzQ 200 grams/liter. H2804 15 grams/liter. Janus Green B .003 gram/ liter. Temperature 70-95 F. Cathode current density 30-40 amps./ sq. ft.

Air agitation.

Example II CuSO4.5HzO 200 grams/liter. H2804; 15 grams/liter. Janus Black .01 gram/liter. Temperatureun 7090 F. Cathode current density 30.40 amps./ sq. ft.

Sodium decyl sulfate .03 gram/liter. Air agitation. 4

Example Ill' Air agitation.

What is claimed is:

1. A bath for the electrodeposition of copper, comprising an aqueous acidic solution of a material selected from the group consisting of copper sulfate and copper nitrate, and minor proportions of a compound having the structure:

wherein R1 and R2 are radicals selected from the group consisting of hydrogen, methyl and ethyl radicals, X is an anion selected from the group consisting of chloride, bromide, iodide, fluoride, sulfate, bisulfate and nitrate, and Z is an aromatic radical selected from the group consisting of phenyl, naphthyl, and phenyl and naphthyl radicals substituted with amino, alkyl substituted ammo, hydroxy and alkoxy substituent groups.

2. A bath for the electrodeposition of copper in the form of a fine grain deposit comprising an aqueous acidic solution of a material selected from the group consisting of copper sulfate and copper nitrate and minor proportions of a compound selected from the group consisting of Janus Green, Janus Blue, Janus Black, Janus Gray, dimethyl safranine azo dimethyl aniline and mixtures thereof.

3. A bath for the electrodeposition of copper, comprising an aqueous acidic solution of a material selected from the group consisting of copper sulfate and copper nitrate, and about .0015 to about .05 gram/liter of a compound having the structure:

wherein R1 and R2 are radicals selected from the group consisting of hydrogen, methyl and ethyl radicals, X is an anion selected from the group consisting of chloride, bromide, iodide, fluoride, sulfate, bisulfate and nitrate, and Z is an aromatic radical selected from the group consisting of phenyl, naphthyl, and phenyl and naphthyl radicals substituted with amino, alkyl'substituted amino, hydroxy and alkoxy substituent groups.

4. A bath for the electrodeposition of copper in the form of a time grain deposit comprising an aqueous acidic ride, bromide, iodide, fluoride, sulfate,

solution of a material selected from the group consisting of copper sulfate and copper nitrate, and about .0015 to .05 gram/liter of a compound selected from the group consisting of Janus Green, Janus Blue, Janus Black, Janus Gray, dimethyl-safranine-azo-dimethyl-aniline and mixtures thereof.

5. A bath for the electrodeposition of copper comprising an aqueous acidic solution of a material selected from the group consisting of copper sulfate and copper nitrate and a minor proportion of Janus Green B.

6. A bath for the electrodeposition of copper comprisin g an aqueous acidic solution of a material selected from the group consisting of copper sulfate and copper nitrate and about .0015 to about .05 gram/liter of Janus Green B.

7. A bath for the electrodeposition of copper in the form of a fine grain deposit comprising an aqueous acidic solution of copper sulfate and .005 to .04 gram/ liter of Janus Green B.

8. In a process of electrodepositing copper, the step which comprises electrolyzing an aqueous acid copper solution containing a metal salt selected from the group consisting of copper sulfate and copper nitrate, said aqueous solution also containing minor proportions of a compound having the structure:

Wherein R1 and R2 are radicals selected from the group consisting of hydrogen, methyl and ethyl radicals, X is an anion selected from the group consisting of chloride, bromide, iodide, fluoride, sulfate, bisulfate and nitrate, and Z is an aromatic radical selected from the group consisting of phenyl, naphthyl, and phenyl and naphthyl radicals substituted with amino, alkyl substituted amino,

ydroxy and alkoxy substituent groups.

9. In a process of electrodepositing copper, the step which comprises electrolyzing an aqueous acidic copper solution containing a metal salt selected from the group consisting of copper sulfate and copper nitrate, said aqueous solution also containing minor proportions of a compound selected from a group consisting of Janus Green B, Janus Black, Janus Gray, Janus Blue, dimethylsafranine-azo-dimethyl-aniline and mixtures thereof.

10. In a process of electrodepositing copper, the step which comprises electrolyzing an aqueous acidic copper solution containing a metal salt selected from the group consisting of copper sulfate and copper nitrate, said aqueous solution also containing about .00l5 to about .05 grams/liter of a compound having the structure:

wherein R1 and R2 are radicals selected from the group consisting of hydrogen, methyl and is an anion selected from the group consisting of chlobisulfate and nitrate, and Z is an aromatic radical selected from the group consisting of phenyl, naphthyl, and phenyl and naphthyl radicals substituted with amino, alkyl substituted amino, hydroxy and alkoxy substituent groups.

11. A bath for the electrodeposition of copper, comprising an aqueous acidic solution of a material selected from the group consisting of copper sulfate and copper nitrate, a halide selected from the group consisting of chloride, bromide and iodide in an amount equivalent ethyl radicals, X

to about .003 gram/liter to about .020 gram/liter of chloride and a minor proportion of a compound having the structure:

wherein R1 and R2 are radicals selected from the group consisting of hydrogen, methyl and ethyl radicals, X is an anion selected from the group consisting of chloride, bromide, iodide, fluoride, sulfate, bisulfate and nitrate, and Z is an aromatic radical selected from the group consisting of phenyl, naphthyl, phenyl and naphthyl radicals substituted with amino, and alkyl substituted amino, hydroxy and alkoxy substituent groups.

12. In a process of electrodepositing copper, the step which comprises electrolyzing an aqueous acidic copper solution containing a metal salt selected from the group consisting of copper sulfate and copper nitrate, a halide selected from the group consisting of chloride, bromide and iodide in an amount equivalent to about .003 gram/ liter to about .020 gram/liter of chloride and a minor proportion of a compound having the structure wherein R1 and R2 are radicals selected from the group consisting of hydrogen, methyl and ethyl radicals, X is an anion selected from the group consisting of chloride, bromide, iodide, fluoride, sulfate, bisulfate and nitrate, and Z is an aromatic radical selected from the group consisting of phenyl, naphthyl, and phenyl and naphthyl radicals substituted with amino, alkyl substituted amino, hydroxy and alkoxy substituent groups.

13. A bath for the electrodeposition of copper, comprising an aqueous acidic solution of a material selected from the group consisting of copper sulfate and copper nitrate, a halide selected from the group consisting of chloride, bromide and iodide in an amount equivalent to about .003 gram/liter to about .020 gram/liter of chloride, a minor proportion of a compound having the structure:

wherein R1 and R2 are radicals selected from the group consisting of hydrogen, methyl and ethyl radicals, X is an anion selected from the group consisting of chloride, bromide, iodide, fluoride, sulfate, bisulfate and nitrate, and Z is an aromatic radical selected from the group consisting of phenyl, naphthyl, phenyl and naphthyl radicals substituted with amino, and alkyl substituted amino, hydroxy and alkoxy substituent groups, and a small amount of a wetting agent.

14. In a process of electrodepositing copper, the step which comprises electrolyzing an aqueous acidic copper solution containing a metal salt selected from the group consisting of copper sulfate and copper nitrate, a halide selected from the group consisting of chloride, bromide and iodide in an amount equivalent to about .003 gram/- liter to about .020 gram/liter of chloride, a minor proportion of a compound having the structure:

wherein R1 and R2 are radicals selected from the group consisting of hydrogen, methyl and ethyl radicals, X is an anion selected from the group consisting of chloride, bromide, iodide, fluoride, sulfate, bisulfate and nitrate, and Z is an aromatic radical selected from the group consisting of phenyl, naphthyl, and phenyl and naphthyl radicals substituted with amino, alkyl substituted amino, hydroxy and alkoxy substituent groups and a small amount of a wetting agent.

References Cited in the file of this patent UNITED STATES PATENTS 2,291,590 Lind et al. July 28, 1942 2,326,999 Lind et al. Aug. 17, 1943 2,602,774 Beaver July 8, 1952 

1. A BATH FOR THE ELECTRODEPOSITION OF COPPER, COMPRISING AN AQUEOUS ACIDIC SOLUTION OF A MATERIAL SELECTED FROM THE GROUP CONSISTING OF COPPER SULFATE AND COPPER NITRATE, AND MINOR PROPORTIONS OF A COMPOUND HAVING THE STRUCTURE: 